Fail-safe systems for respirating gas delivery devices

Abstract

A fail-safe system for use with pulse dose respirating gas delivery devices provides a continuous, metered flow of oxygen to the patient in the event that the delivery device malfunctions or suffers a power failure. The system includes a piston resiliently biased toward one end of a cylinder and having provision for applying the force of pressurized respirating gas on the piston in opposition to the biasing force and in synchronization with doses of respirating gas produced by the delivery device and to remove that force in coordination with the delivery of a gas dose to the patient. The piston movement is arranged to actuate valve means opening a path for the continuous flow of oxygen to the patient in the event that successive gas doses are not delivered to the patient within a predetermined length of time.

I claim: 
     
       1. A fail-safe device for pulse dose respirating gas delivery systems, said device adapted to provide continuous gas flow to a patient in the event of system malfunction, comprising: a movable piston disposed within a cylinder, said piston urged toward a first end of said cylinder by resilient biasing means;   means to periodically apply the force of pressurized respirating gas to the piston end opposite said biasing means in synchronization with doses of respirating gas produced by said system for delivery to a patient, the force produced by said pressurized respirating gas being sufficiently great to cause said piston to overcome the force of said biasing means and move toward the other cylinder end;   means to relieve the force of said gas upon said piston end in coordination with the cycling by the system in its delivery of gas doses to the patient thereby causing said piston to return toward said first cylinder end by action of said biasing means; and   valve means actuated by movement of said piston to a specific position within said cylinder, the arrival of said piston at said specific position arranged to occur a predetermined length of time after delivery of a gas dose to the patient, said valve means when activated arranged to deliver a continuous metered stream of respirating gas to the patient.   
     
     
       2. The device of claim 1 wherein said means to relieve the force of gas upon said piston end acts after delivery of a gas dose to the patient. 
     
     
       3. The device of claim 1 wherein said means to relieve the force of gas upon said piston end acts upon delivery of a gas dose to the patient. 
     
     
       4. The device of claim 1 wherein said pulse dose gas delivery system is of the rate-time metering type. 
     
     
       5. The device of claim 1 wherein said pulse dose gas delivery system is of the volumetric metering type. 
     
     
       6. The device of claim 5 wherein said force of pressurized respirating gas is applied through a mechanical connection to said piston end. 
     
     
       7. The device of claim 5 wherein said force of pressurized respirating gas is pneumatically applied to said piston end. 
     
     
       8. A fail-safe device for pulse dose respirating gas delivery systems, said device adapted to provide continuous gas flow to a patient in the event of system malfunction, comprising: a movable piston disposed within a cylinder, said piston urged toward a first end of said cylinder by resilient biasing means;   means to periodically supply respirating gas to the interior end of said cylinder opposite said biasing means in synchronization with doses of respirating gas produced by said system for delivery to a patient, the pressure of said supplied respirating gas being sufficiently high to cause said piston to overcome the force of said biasing means and to move toward the other cylinder end;   means to relieve the gas pressure within said cylinder in coordination with the cycling by the system in its delivery of gas doses to the patient thereby causing said piston to return toward said first cylinder end by action of said biasing means; and   valve means actuated by movement of said piston to an extreme position opposite said first cylinder end, the arrival of said piston at said extreme position arranged to occur a predetermined length of time after delivery of a gas dose to the patient, said valve means when activated arranged to deliver a continuous metered stream of respirating gas to the patient.   
     
     
       9. The device of claim 8 wherein said pulse dose gas delivery system employs a two-position valve for rate-time metering, said valve in the first of said positions delivering a bleed stream of gas to the interior of said cylinder and, in the second of said positions, producing a pulse dose of gas for delivery to said patient while at the same time relieving the gas pressure within said cylinder 
     
     
       10. The device of claim 9 wherein said valve means comprise two ports in the wall of said cylinder, one of said ports communicating with the supply of said respirating gas and the other of said ports communicating with conduit means arranged for delivery of gas doses to the patient, said ports normally covered by said piston but uncovered upon arrival of said piston at said extreme position. 
     
     
       11. The device of claim 10 wherein said means to relieve the pressure within said cylinder includes a by-pass line around a check valve, said by-pass line having a bleed orifice limiting the rate of flow of gas to said cylinder and said check valve arranged to allow flow only from said cylinder. 
     
     
       12. The device of claim 11 including a capacitance adapted to increase the size of the gas dose delivered to the patient as the breathing rate of the patient decreases, said capacitance comprising a chamber arranged in parallel with said cylinder and located between said check valve and said cylinder, said chamber adapted to be filled through said bleed orifice and emptied through said check valve. 
     
     
       13. The device of claim 8 wherein said pulse dose gas delivery system is a double-acting volumetric displacer comprising a closed cylinder having a piston disposed therein, said piston free to move from one cylinder end to the other. 
     
     
       14. The device of claim 13 including conduit means communicating between a port located in the wall of said displacer cylinder at a point midway between its ends and the interior end of said fail-safe device cylinder, said conduit having a check valve located therein, said check valve allowing flow only toward said displacer cylinder port. 
     
     
       15. The device of claim 14 wherein a by-pass line is provided around said check valve, said by-pass line having a bleed orifice therein, said orifice adapted to allow a slow flow of gas around said check valve. 
     
     
       16. The device of claim 15 wherein said valve means comprise two ports in the wall of said cylinder, one of said ports communicating with the supply of said respirating gas and the other of said ports communicating with conduit means arranged for delivery of gas doses to the patient, said ports normally covered by said piston but uncovered upon arrival of said piston at said extreme position. 
     
     
       17. The device of claim 8 wherein said pulse dose gas delivery system is a volumetric metering displacer comprising a piston operating within a cylinder, said piston urged toward one end of the cylinder by resilient restoring means. 
     
     
       18. The device of claim 17 including a two-position flow control valve, said valve in its first position connecting the supply of said respirating gas through conduit means to the interior end of said displacer cylinder opposite said resilient restoring means and to the interior end of said fail-safe device cylinder opposite said biasing means, said valve in its second position isolating said supply of respirating gas from the system and connecting said displacer cylinder and said fail-safe cylinder to conduit means adapated to convey gas to the patient. 
     
     
       19. The device of claim 18 wherein the biasing means of said cylinder comprises a compartment having vent means, said vent means including a bleed orifice and a check valve, said bleed orifice adapted to restrict the flow of gas out of said compartment and said check valve arranged to permit rapid gas flow into said compartment. 
     
     
       20. The device of claim 19 wherein said valve means comprise a port in the side wall of said cylinder, said port communicating with conduit means arranged for delivery of gas doses to the patient, said port normally covered by said piston but uncovered to allow a continuous flow of gas to the patient upon arrival of said piston at its extreme position. 
     
     
       21. The device of claim 17 including rod means attached to said displacer piston and adapted to limit the travel of said piston. 
     
     
       22. The device of claim 21 wherein the travel of said piston is limited by stop means arranged to engage an end of said rod means. 
     
     
       23. The device of claim 21 including rod means attached to the movable piston of said fail-safe system at the piston end opposite said biasing means, said rod means arranged to engage the end of that rod means attached to said displacer piston and to limit the travel of said displacer piston. 
     
     
       24. The device of claim 23 wherein said valve means comprise a port in the side wall of said displacer cylinder, said port communicating with conduit means arranged for delivery of gas doses to the patient, said port normally covered by said displacer piston but uncovered to allow a continuous flow of gas to the patient when the piston of said fail-safe device is moved to its extreme position under the force of said displacer piston delivered through said rod means. 
     
     
       25. The device of claim 8 wherein said pulse dose gas delivery system is a volumetric metering displacer comprising a metering chamber of fixed volume, said chamber adapted to be filled with respirating gas at a set pressure above atmospheric to provide a single dose quantity, and wherein delivery of said dose to the patient is powered by expansion of the gas within said chamber. 
     
     
       26. A respirating gas delivery system for providing pulsed doses of respirating gas to a patient and for providing a continuous gas flow to the patient in case of system malfunction comprising: a source of respirating gas at a controlled pressure above atmospheric;   means to produce pulsed doses of said respirating gas in coordination with the respiratory cycle of the patient;   passage means to deliver said pulsed gas doses to the patient;   a chamber arranged with a movable sealing means, the position of said sealing means responding to changes in pressure within said chamber and resiliently biased in a manner which tends to reduce the internal volume of said chamber, said sealing means further arranged to move to an extreme position in the absence for a predetermined period of time of pressure variations within the chamber; means for varying the pressure within said chamber in coordination with the cyclic variations in pressure within said passage means which result from delivery of said pulsed gas doses through said passage means, the variations of said chamber pressure causing movement of said sealing means;     flow control means adapted to open a metered flow path from said respirating gas source to the patient when said sealing means has moved to its extreme position as a result of cessation of said cyclic pressure variations.   
     
     
       27. In a method wherein a pulse dose respirating gas delivery system is used to deliver measured doses of a pressurized respirating gas to a patient in synchronization with the respiratory cycle of the patient and wherein a continuous metered flow of said respirating gas is provided to the patient in the event that said pulse dose delivery system malfunctions, the improvement comprising: providing a valve means having a resilient bias, said valve means being movable from one position another;   periodically applying said pressurized respirating gas to said valve means, said pressurized respirating gas applying a force to the valve means which opposes the resilient bias of said valve means; and   providing doses of respirating gas produced by the delivery system to the patent;   relieving said force upon the valve means upon delivery of gas doses to the patient;   applying said force to said valve means thereby causing said valve means to open a path for the continuous flow of respirating gas to the patient in the event that said pulse dose delivery system fails to deliver a gas dose to the patient within a predetermine period of time.   
     
     
       28. The method of claim 27 wherein the force upon said valve means is relieved after the delivery of said gas dose to the patient. 
     
     
       29. The method of claim 27 wherein the force of pressurized respirating gas is pneumatically applied to said valve means. 
     
     
       30. The method of claim 27 wherein the force of pressurized respirating gas is mechanically applied to said valve means. 
     
     
       31. The method of claim 27 wherein the size of the gas dose delivered to the patient is increased as the breathing rate of the patient decreases. 
     
     
       32. In a method wherein a pulse dose respirating gas delivery system is used to deliver measured doses of a pressurized respirating gas to a patient in synchronization with the respiratory cycle of the patient and wherein a continuous metered flow of said respirating gas is provided to the patient in the event that said pulse does delivery system malfunctions, the improvement comprising: providing a valve means having a resilient bias, said valve means being movable from one position to another;   periodically applying said pressurized respirating gas to said valve means, said pressurized respirating gas applying a force to the valve means which opposes the resilient bias of said valve means; and   providing doses of respirating gas produced by the delivery system to the patient;   relieving said force upon the valve means upon delivery of gas doses to the patient;   relieving said force on said valve means thereby causing said valve means to open a path for the continuous flow of respirating gas to the patient in the event that said pulse dose delivery system fails to deliver a gas dose to the patient within a predetermined period of time.